1. Field of the Invention
This invention relates to an apparatus for carrying out operations at underwater installations and pertains more particularly to an apparatus for manipulating equipment in the vicinity of, or which components are located on, an underwater installation, such for example as an underwater wellhead, an underwater oil and gas production facility, storage facilities, etc.
2. Description of the Prior Art
A recent development at offshore locations is the installation of large amounts of equipment underwater used in the production of oil fields and gas fields situated many miles from shore. Many wells are being built in water depths up to 6,000 feet deep, a depth greater than divers can safely work. Thus, in drilling wells, producing wells, installing underwater equipment on the ocean floor, and carrying out workover operations underwater at any of the various ocean floor installations, use has been made of what is known as a manipulator apparatus for gripping submerged objects such as the particular pieces forming the underwater equipment.
Consideration has been given to the use of magnets or electromagnets carried by such a manipulator apparatus by which the manipulator apparatus could be secured to an underwater installation during the time it is carrying out a particular operation thereon. However, in order to combat seawater corrosion, there has been a tendency to make more of the underwater equipment of stainless steel on which electromagnets cannot be used to mount a magnetic manipulator apparatus.
Such gripping devices as set forth in U.S. Pat. No. 3,165,899 issued Jan. 19, 1965, to H. L. Shatto, Jr., and as set forth in U.S. Pat. No. 3,720,433 issued Mar. 13, 1973, to A. M. Rosfelder, disclose such apparatus using primarily suction cups which attach to the underwater object to be manipulated. The suction cups disclosed however, in both of these patents have their suction cavities open to the body of water in which the underwater objects are located. Suction applied through each cup loosens foreign material under the cup and causes the loosened material to be drawn upwards into the pumping system that generates suction at the face of each cup. Such an open suction cup design also requires continuous use of pumping power to compensate for leakage around each suction cup that contacts the underwater object. Additionally, cups which do not contact the underwater object continuously draw in additional sea water which decreases the overall suction gripping force of the entire apparatus.
An apparatus need be disclosed, therefore, that does not require a continuous pumping action upon the face of the suction cups in order to maintain a suction grip upon the underwater object. Such an apparatus should also not ingest within the pumping equipment any foreign material loosened by the suction cup. Such an apparatus should also have a means for sealing off suction cups which are not in contact with the underwater object by means of a device more reliable and more simple than the needle valve arrangement shown, for example, in FIG. 8 of Patent '433.